Abstract: A testing chuck for providing a thermally controlled mounting for wafer scale integrated circuits includes a body having a flat upper surface, upon which the integrated circuit is mounted, cooled or heated by a fluid flowing through a number of channels formed in the body. The channels have entrance and exit ends fluidly connected to first entrance and exit plenums. Second entrance and exit plenums are connected to the first entrance and exit plenums by a number of entrance and exit distribution conduits. Fluid is pumped into the second entrance plenum, through the entrance distribution conduits, through the first entrance plenum and into the entrance ends of the channels. After passing through the channels, the fluid flows through the first exit plenum, exit distribution conduits and second exit plenum. The entrance and exit plenums are curved in the direction of fluid flow to reduce stagnant regions within the plenums to aid heat transfer and draining of the chuck.