Green's functions play an important role in electroelastic analyses of piezoelectric media. However, most works available on the topic are for the case of uniform temperature. Based on the compact 2-D general solution of orthotropic piezothermoelectric material, which is expressed in harmonic functions, and employing the trial-and-error method, the 2-D Green's function for a steady line heat source in a semi-infinite piezothermoelectric plane is presented by four newly induced harmonic functions. All components of the coupled field are expressed in terms of elementary functions and are convenient to use. Numerical results are given graphically by contours.