-The performance of RF hot-via transitions for use in chip-scale package (CSP) MMICs are presented. This is illustrated with the realization of a low noise amplifier MMIC using optimized hot-vias. Based on our standard 0.25-µm GaAs low-noise PHEMT process, with BCB coating and backside metallization, this 2-stage low noise microstrip amplifier mounted with bumps on a carrier substrate achieved a linear gain of 15 dB over the 15-to 32 GHz frequency range. To the author's knowledge, this is the first demonstration of chip-scale packaged active MMICs using hot-via transitions.