Results from optically detected cyclotron resonance (ODCR) studies of electron effective masses in 4H SiC are reported. ODCR measurements were performed on high‐purityn‐type 4H SiC epitaxial layers grown by chemical vapor deposition at bothXband (9.23 GHz) andQband (35.05 GHz) microwave frequencies. Electron effective masses in 4H SiC were directly determined asm⊥*=0.42m0andm∥*=0.29m0. A scattering time in the basal plane &tgr;⊥≊4.3×10−11s, and hence, the corresponding electron mobility &mgr;⊥≊1.8×105cm2/V s, was obtained from a fit of the ODCR line shape. ©1995 American Institute of Physics.