We have developed a sensitive method for detecting hot spots in LSIs, which is called Dye Thermochromism Imaging (DTI). A key is a thermochromic dye film based on a leuco-dye/acid/modulator/polymer system. The blue color of this film reversibly fades at temperatures near room temperature: its transmittance at 610 nm changes at a logarithmic slope of 0.35/°C. A differential local brightness increase in the image indicates a hot spot when an LSI is biased with a supply voltage. We observed a hot spot in a low power SRAM at supply voltages between 0.9 and 2 V and power dissipations between 0.072 and 1 mW using a 10-bit/12-bit dual mode CCD. Comparing DTI with fluorescent microthermal imaging (FMI), we found that DTI has several advantages with regard to temperature sensitivity, reproducibility in repeated measurements, instrumental setup, and speed of measuring.