This paper describes a method to measure thermal diffusivity of laser diodes simultaneously with thermal resistance of their adhesive joints. The method is based on analysis of temperature variations of emitting regions caused by a quasi-continuous heat generation. A constant input power is applied in the laser diode during several seconds and switched off during some milliseconds. Temperature variations are detected during short sequences from about 10(-6) up to 10(-3) s. Temperatures are obtained from terminal, voltage measurements resulting from injection of a small current. A steady state is reached during each large sequence and each short sequence can be then regarded as a transient state. Parameter identification uses a multidimensional heat diffusion model. Results have been obtained on a multistripe double heterostructure GaAs/GaAlAs laser diode owing ten emitting zones of 4 mu m width. Thermal diffusivity of the substrate (N-GaAs) and thermal resistance of its adhesive joint have been identified. In addition, this method allows one to estimate steady slate junction temperature and output optical power as a function of input current intensity.