The development and characterization of a medium depth Si trench process for power IC applications, was performed utilizing Self-Excited Electron Resonance Spectroscopy (SEERS). SEERS provides volume averaged plasma parameters such as electron collision frequency, electron density and sheath width by monitoring the non-linearity of the space charge sheath at the electrode. Several etch chemistries were investigated including SF@sub 6@/ O@sub 2@, Cl@sub 2@/ O@sub 2@, HBr/ O@sub 2@, HBr/SF@sub 6@/O@sub 2@ and Cl@sub 2@/SF@sub 6@/O@sub 2@ and their effect on etch rate and sidewall profile. Pressure appears to be the overwhelming parameter in terms of profile and has a large effect on the electron collision rate and electron heating mechanisms. The study of pressure effects on electron temperatures and electron collision rates have been performed@footnote 1@ but these parameters have yet to be correlated to the actual etch performance and trench morphology. This study looks at these relationships and their effects on the optimized trench process.