An apparatus for cooling at least one heated surface includes a base plate defining a number of inlet and outlet manifolds. The inlet manifolds are configured to receive a coolant, and the outlet manifolds exhaust the coolant. The inlet and outlet manifolds are interleaved. The apparatus also includes at least one substrate having inner and outer surfaces. The inner surface is coupled to the base plate and defines a number of microchannels that receive the coolant from the inlet manifolds and deliver the coolant to the outlet manifolds. The microchannels are oriented substantially perpendicular to the inlet and outlet manifolds. The outer surface is in thermal contact with the heated surface. The apparatus also includes an inlet plenum that supplies the coolant to the inlet manifolds, and an outlet plenum that exhausts the coolant from the outlet manifolds. The inlet plenum and outlet plenum are oriented in a plane of the base plate.