Ever increasing importance of cooling and precise temperature control in microelectronics and optoelectronics has driven recent development of integrated thermoelectric and thermionic cooling structures. Previous studies have investigated SiGe/Si superlattice thermionic coolers experimentally using thermocouples that were 50 μm in diameter. However, the relative size of these thermocouples as compared to the devices sizes (30–100 μm) makes surface and cross-section temperature measurement of the SiGe/Si superlattice thermionic coolers not possible. In this work, a sub 100 nm probe was used to measure the surface and cross-sectional temperature of the SiGe/Si superlattice thermionic coolers using scanning thermal microscopy. Two sets of superlattice thermionic coolers were used in this study and their cooling curves (temperature vs current) are presented. Each set consists of six devices of different sizes. A comparison of device cooling performance is examined. A mechanism for studying thermionic cooling in the superlattice coolers is discussed through an analysis of the cooler cross-section temperature profile.