We have used C-V techniques to study the bias instability of 4H-SiC MOS capacitors and FETs, and compared those results to those obtained using ID-VGS. The net “back-and-forth” instability from C-V was found to exceed that of ID-VGS and matched closely with values from fast ID-VGS and midgap extrapolation, suggesting that the C-V method is more effective at measuring a “true” instability effect than ID-VGS alone. Using C-V, capacitors and large-area MOSFETs showed similar instability behavior, implying that the presence of minority carriers are not necessary to observe bias instability. One-way bias-stress C-V measurements reveal that most of the bias instability occurs under negative bias stress, whereas the opposite is observed in one-way bias stress ID-VGS measurements. Finally, post-oxidation NO annealing reduced the ΔVT bias instability for positive bias stress but does not appear to have influenced any of the other conditions.