a multi - well plate is disclosed for holding chemical compounds for heating in a microwave oven . the plate is a substantially planar member having wells arranged in an array of rows and columns in its upper surface . the plate has heat reservoirs in the form of fluid filled channels or elongated solid bodies positioned lengthwise along the side portions of the plate to reduce temperature gradients among the wells across the length and width of the plate . the heat reservoirs prevent or mitigate heat loss from the wells near the side portions of the plate and ensure that the compounds in all of the wells have a uniform temperature .