A thermal interposer is provided for attachment to a surface of a semiconductor device. In one embodiment, the thermal interposer includes an upper plate having a bottom surface with a plurality of grooves and made of a material having high thermal conductivity, and a lower plate having a top surface with a plurality of grooves and made of a material having a coefficient of thermal expansion that is substantially the same as the coefficient of thermal expansion of the material of a semiconductor device that is bonded to the bottom surface of the lower plate. The bottom surface of the upper plate is hermetically bonded to the top surface of the lower plate so that a vapor chamber is formed by the upper and lower plates, and walls of the grooves on the top surface of the lower plate extend to within less than 250 microns from walls of the grooves on the bottom surface of the upper plate comprise a plurality of second walls the first walls.