diff --git a/src/py_dvt_ate/simulation/physics/models/base.py b/src/py_dvt_ate/simulation/physics/models/base.py
new file mode 100644
index 0000000..c2fed0b
--- /dev/null
+++ b/src/py_dvt_ate/simulation/physics/models/base.py
@@ -0,0 +1,61 @@
+"""Base protocol for Device Under Test (DUT) models.
+
+Defines the interface that all DUT models must implement to integrate
+with the physics engine.
+"""
+
+from typing import Protocol, runtime_checkable
+
+
+@runtime_checkable
+class DUTModel(Protocol):
+    """Protocol for DUT electrical/thermal models.
+
+    DUT models encapsulate the temperature-dependent electrical behaviour
+    of a device, enabling realistic simulation of thermal-electrical coupling.
+
+    All temperature parameters are in degrees Celsius.
+    All voltage parameters are in volts.
+    All current parameters are in amps.
+    All power parameters are in watts.
+    """
+
+    def calculate_output_voltage(self, junction_temperature: float) -> float:
+        """Calculate the output voltage at the given junction temperature.
+
+        Args:
+            junction_temperature: DUT junction temperature in degrees Celsius.
+
+        Returns:
+            Output voltage in volts.
+        """
+        ...
+
+    def calculate_quiescent_current(self, junction_temperature: float) -> float:
+        """Calculate the quiescent current at the given junction temperature.
+
+        Args:
+            junction_temperature: DUT junction temperature in degrees Celsius.
+
+        Returns:
+            Quiescent current in amps.
+        """
+        ...
+
+    def calculate_power_dissipation(
+        self,
+        input_voltage: float,
+        load_current: float,
+        junction_temperature: float,
+    ) -> float:
+        """Calculate the power dissipation for given operating conditions.
+
+        Args:
+            input_voltage: Input voltage in volts.
+            load_current: Load current in amps.
+            junction_temperature: DUT junction temperature in degrees Celsius.
+
+        Returns:
+            Power dissipation in watts.
+        """
+        ...