A power unit for an electrical steering system includes a motor housing for accommodating a motor, a heat sink and a drive electronics system, which is arranged on the heat sink, for the motor. The heat sink and the motor housing are connected to one another in such a way that heat exchange from the drive electronics system, via the heat sink, to the motor housing is possible. The heat sink is at least partially connected to the motor housing by calking or welding or screwing. A method is used for assembling a power unit having a motor housing for accommodating a motor, a heat sink and a drive electronics system, which is arranged on the heat sink, for the motor. A connection is established between the heat sink and the motor housing by calking or welding or screwing.