A test structure for analysis of temperature distribution in CMOS LSI is presented. Fundamental thermal properties of LSI chip were measured and discussed with simulation results. The test structure consists of 24 sensor blocks, each of which has a resistor as an on-chip heater, a p-n diode array for temperature sensing and selector switches. Dependence of heating time and distance from the resistor were analyzed as well as transient phenomena. The test structure can provide an effective methodology for analysis of fundamental thermal properties in LSIs packaged in various ways.