The picosecond pulses of hot carrier luminescence that are observed from individual submicron FETs in CMOS circuits can be used to describe the internal operation of integrated circuits. To effectively use the weak emission pulses, we have developed a method called picosecond integrated circuit analysis (PICA) which simultaneously images and time resolves the emission. PICA has been used to characterize the operation of integrated circuits from simple ring oscillators to a full microprocessors. Examples of circuit characterization and fault diagnosis are presented.