We revisit the mechanism leading to the photoresponse of locally illuminated single-walled carbon nanotube (SWNT) films deposited on substrates. Our study examines the impact of multiple device parameters and provides many evidences that the position-dependent photocurrent is dominated by photothermoelectric effects. The photoresponse arises from the temperature variations at the metal–nanotube film interfaces, where mismatches of the Seebeck coefficients are measured. Our work also stresses the impact of the substrates, electrode materials and post-thermal treatments on the amplitude and dynamics of the photoresponse. The knowledge gained should guide the future development of photothermoelectric devices and detectors based on SWNTs.