Kelvin probe force microscopy (KPFM) is a unique technique that can provide two dimensional potential profiles inside a working device. A procedure is described to obtain high-resolution KPFM results on ultra-high vacuum (UHV) cleaved III-V MOSCAPs. Two tip preparation methods: field emission and Cr coating show reproducible high spatial and energy resolution KPFM images. A unique sample design has been developed which is compatible with UHV cross-sectional KPFM (x-KPFM). Key design features are high density of devices on the cleave face, a buried device interface, and a cleavable gate contact. Using x-KPFM, the first UHV cleaved MOSCAP surface potential mapping is demonstrated.