Passive diamond layers fabricated using chemical vapor deposition can improve thermal conduction in electronic microstructures. The benefit of using diamond depends strongly on the thermal boundary resistance between active semiconducting regions, where heat is generated, and the diamond. Two independent experimental methods measure the total thermal resistance for conduction normal to 0.2, 0.5, and 2.6 &mgr;m thick diamond layers deposited on silicon, providing an upper bound for the effective silicon‐diamond boundary resistance. The data agree with predictions that couple the local phonon scattering rate in the diamond to the grain size. ©1995 American Institute of Physics.