The interaction of plasmon surface polaritons (PSPs) with the tunneling junction of a scanning tunneling microscope (STM) has been investigated by measuring the current response to a modulated plasmon excitation. From the dependence on modulation frequency, bias voltage, steady‐state current, and metal film structure it is concluded that it originates mainly from PSP‐induced heating and the associated expansion of the tunneling tip. The modulated current signal (or the equivalently modulatedz‐piezo voltage after the feedback loop) can be recorded while scanning the surface by STM. The resulting PSP maps reflect the polycrystalline metal film structure on the scale of a few nanometers convoluted to some extent with the tip shape and the PSP field distribution. The latter can be used to differentiate between different metal films on the micrometer scale.