The on-resistance of a power metal-oxide semiconductor held-effect transistor device was found to differ dramatically based on substrate supplier. Differences in substrate resistance could not account for the observed change in the total del iee on-resistance, R-DS(ON), Other possible factors, bulk microdefects generated by oxygen precipitation and drain contact resistance, could affect the observed difference in R-DS(ON) and were investigated accordingly. Substrates from three different suppliers with and without the addition of a 2 h, 700 degrees C precipitation nucleation heat cycle were compared. The difference in bulk microdefect densities between the substrates could not account for the observed change in R-DS(ON). By adding an aluminum backmetal layer prior to the deposition of the TiNiAg backmetal, R-DS(ON) was decreased regardless of the prebackmetal cleaning process. This revealed that the effect of substrate resistivity on the contact resistance of backmetal was the dominant cause of R-DS(ON) discrepancies between the substrates.