This article presents an overview for the development of GaN and other III-V PAs with built-in temperature and load sensing to monitor reliability and performance factors. Supply voltage can be a significant fraction of the device breakdown voltage. High temperature conditions may be present. Load mismatch and unintended resonances may cause high drain voltage swings. In situ measurement of temperature and load impedance or VSWR allow PA operation with tighter design margins. Temperature sensing techniques developed do not require on-chip device modeling. Multiport reflectometry techniques developed to monitor load impedance introduce no components in the RF path. An all-analogue technique to monitor VSWR requires no substantial computation.