A coolant distribution structure for an MMIC having: an input/output layer with an input port for receiving a coolant for transmission to coolant channels in the MMIC and an output port for exiting the coolant after such coolant has cooled active devices in the MMIC, a coolant pass-through layer to receive the coolant from the input port and having structure to inhibit such received coolant from passing directly to the output port, a coolant distribution layer for receiving coolant passing from the coolant pass-through layer and distributing such received coolant to the cooling channels to absorb heat generated by the active devices and then directing heated coolant to the coolant distribution layer and out of the porting layer via the passthrough layer. The coolant pass-through layer has a structure configured to inhibit such heated coolant from passing directly to the input port prior to such heated absorbed coolant being transmitted to the output port.