diff --git a/esphome/components/debug/debug_zephyr.cpp b/esphome/components/debug/debug_zephyr.cpp
index 85880595b6..3f9af03b2b 100644
--- a/esphome/components/debug/debug_zephyr.cpp
+++ b/esphome/components/debug/debug_zephyr.cpp
@@ -322,6 +322,8 @@ size_t DebugComponent::get_device_info_(std::span<char, DEVICE_INFO_BUFFER_SIZE>
     return "Unspecified";
   };
 
+  char mac_pretty[MAC_ADDRESS_PRETTY_BUFFER_SIZE];
+  get_mac_address_pretty_into_buffer(mac_pretty);
   ESP_LOGD(TAG,
            "Code page size: %u, code size: %u, device id: 0x%08x%08x\n"
            "Encryption root: 0x%08x%08x%08x%08x, Identity Root: 0x%08x%08x%08x%08x\n"
@@ -330,10 +332,10 @@ size_t DebugComponent::get_device_info_(std::span<char, DEVICE_INFO_BUFFER_SIZE>
            "RAM: %ukB, Flash: %ukB, production test: %sdone",
            NRF_FICR->CODEPAGESIZE, NRF_FICR->CODESIZE, NRF_FICR->DEVICEID[1], NRF_FICR->DEVICEID[0], NRF_FICR->ER[0],
            NRF_FICR->ER[1], NRF_FICR->ER[2], NRF_FICR->ER[3], NRF_FICR->IR[0], NRF_FICR->IR[1], NRF_FICR->IR[2],
-           NRF_FICR->IR[3], (NRF_FICR->DEVICEADDRTYPE & 0x1 ? "Random" : "Public"), get_mac_address_pretty().c_str(),
-           NRF_FICR->INFO.PART, NRF_FICR->INFO.VARIANT >> 24 & 0xFF, NRF_FICR->INFO.VARIANT >> 16 & 0xFF,
-           NRF_FICR->INFO.VARIANT >> 8 & 0xFF, NRF_FICR->INFO.VARIANT & 0xFF, package(NRF_FICR->INFO.PACKAGE),
-           NRF_FICR->INFO.RAM, NRF_FICR->INFO.FLASH, (NRF_FICR->PRODTEST[0] == 0xBB42319F ? "" : "not "));
+           NRF_FICR->IR[3], (NRF_FICR->DEVICEADDRTYPE & 0x1 ? "Random" : "Public"), mac_pretty, NRF_FICR->INFO.PART,
+           NRF_FICR->INFO.VARIANT >> 24 & 0xFF, NRF_FICR->INFO.VARIANT >> 16 & 0xFF, NRF_FICR->INFO.VARIANT >> 8 & 0xFF,
+           NRF_FICR->INFO.VARIANT & 0xFF, package(NRF_FICR->INFO.PACKAGE), NRF_FICR->INFO.RAM, NRF_FICR->INFO.FLASH,
+           (NRF_FICR->PRODTEST[0] == 0xBB42319F ? "" : "not "));
   bool n_reset_enabled = NRF_UICR->PSELRESET[0] == NRF_UICR->PSELRESET[1] &&
                          (NRF_UICR->PSELRESET[0] & UICR_PSELRESET_CONNECT_Msk) == UICR_PSELRESET_CONNECT_Connected
                                                                                       << UICR_PSELRESET_CONNECT_Pos;
diff --git a/esphome/components/mqtt/mqtt_client.cpp b/esphome/components/mqtt/mqtt_client.cpp
index 652f55734b..0ab5b238b5 100644
--- a/esphome/components/mqtt/mqtt_client.cpp
+++ b/esphome/components/mqtt/mqtt_client.cpp
@@ -28,8 +28,9 @@ static const char *const TAG = "mqtt";
 
 MQTTClientComponent::MQTTClientComponent() {
   global_mqtt_client = this;
-  const std::string mac_addr = get_mac_address();
-  this->credentials_.client_id = make_name_with_suffix(App.get_name(), '-', mac_addr.c_str(), mac_addr.size());
+  char mac_addr[MAC_ADDRESS_BUFFER_SIZE];
+  get_mac_address_into_buffer(mac_addr);
+  this->credentials_.client_id = make_name_with_suffix(App.get_name(), '-', mac_addr, MAC_ADDRESS_BUFFER_SIZE - 1);
 }
 
 // Connection
@@ -102,7 +103,9 @@ void MQTTClientComponent::send_device_info_() {
         root[ESPHOME_F("port")] = api::global_api_server->get_port();
 #endif
         root[ESPHOME_F("version")] = ESPHOME_VERSION;
-        root[ESPHOME_F("mac")] = get_mac_address();
+        char mac_buf[MAC_ADDRESS_BUFFER_SIZE];
+        get_mac_address_into_buffer(mac_buf);
+        root[ESPHOME_F("mac")] = mac_buf;
 
 #ifdef USE_ESP8266
         root[ESPHOME_F("platform")] = ESPHOME_F("ESP8266");
diff --git a/esphome/components/mqtt/mqtt_component.cpp b/esphome/components/mqtt/mqtt_component.cpp
index d838d1789f..40eb15acdd 100644
--- a/esphome/components/mqtt/mqtt_component.cpp
+++ b/esphome/components/mqtt/mqtt_component.cpp
@@ -187,7 +187,13 @@ bool MQTTComponent::send_discovery_() {
           char friendly_name_hash[9];
           sprintf(friendly_name_hash, "%08" PRIx32, fnv1_hash(this->friendly_name_()));
           friendly_name_hash[8] = 0;  // ensure the hash-string ends with null
-          root[MQTT_UNIQUE_ID] = get_mac_address() + "-" + this->component_type() + "-" + friendly_name_hash;
+          // Format: mac-component_type-hash (e.g. "aabbccddeeff-sensor-12345678")
+          // MAC (12) + "-" (1) + domain (max 20) + "-" (1) + hash (8) + null (1) = 43
+          char unique_id[MAC_ADDRESS_BUFFER_SIZE + ESPHOME_DOMAIN_MAX_LEN + 11];
+          char mac_buf[MAC_ADDRESS_BUFFER_SIZE];
+          get_mac_address_into_buffer(mac_buf);
+          snprintf(unique_id, sizeof(unique_id), "%s-%s-%s", mac_buf, this->component_type(), friendly_name_hash);
+          root[MQTT_UNIQUE_ID] = unique_id;
         } else {
           // default to almost-unique ID. It's a hack but the only way to get that
           // gorgeous device registry view.
@@ -203,7 +209,8 @@ bool MQTTComponent::send_discovery_() {
         std::string node_area = App.get_area();
 
         JsonObject device_info = root[MQTT_DEVICE].to<JsonObject>();
-        const auto mac = get_mac_address();
+        char mac[MAC_ADDRESS_BUFFER_SIZE];
+        get_mac_address_into_buffer(mac);
         device_info[MQTT_DEVICE_IDENTIFIERS] = mac;
         device_info[MQTT_DEVICE_NAME] = node_friendly_name;
 #ifdef ESPHOME_PROJECT_NAME
diff --git a/esphome/core/helpers.h b/esphome/core/helpers.h
index 396a58464f..8847586f0a 100644
--- a/esphome/core/helpers.h
+++ b/esphome/core/helpers.h
@@ -1306,9 +1306,13 @@ class HighFrequencyLoopRequester {
 void get_mac_address_raw(uint8_t *mac);  // NOLINT(readability-non-const-parameter)
 
 /// Get the device MAC address as a string, in lowercase hex notation.
+/// @warning Allocates heap memory. Avoid in new code - causes heap fragmentation on long-running devices.
+/// Use get_mac_address_into_buffer() instead.
 std::string get_mac_address();
 
 /// Get the device MAC address as a string, in colon-separated uppercase hex notation.
+/// @warning Allocates heap memory. Avoid in new code - causes heap fragmentation on long-running devices.
+/// Use get_mac_address_pretty_into_buffer() instead.
 std::string get_mac_address_pretty();
 
 /// Get the device MAC address into the given buffer, in lowercase hex notation.