The effective mobility in 4H-SiC trench metal-oxidesemiconductor field-effect transistors (MOSFETs) with an n-channel region on the (1100) face, corresponding to the trench sidewalls, is investigated. Using a previously proposed mobility model, which includes Coulomb scattering mobility (mu(C)), surface roughness scattering mobility (mu(SR)) and optical phonon scattering mobility (mu(OP)), the dependence of the effective field (E-eff) on mu(OP) is studied experimentally. It is found that for the trench MOSFETs with a drift layer, mu(OP) is proportional to Eeff(-1), whereas for trench MOSFET without a drift layer, it is proportional to E-eff(-0.3), which is consistent with reports on phonon scattering mobility in SiC lateral MOSFETs fabricated on (0001) and (0001) faces. The results suggest that the proposed mobility model is effective, and that the dependence of E-eff on mu(OP) is not affected by the plane orientation of SiC and needs to be evaluated with the drift layer resistance removed. A method for evaluating the carrier transport properties of trench MOSFETs with a drift layer is also proposed.