Methods for a new, drug-free therapy for treating solid skin tumors through the application of nanosecond pulsed electric fields (“nsPEFs”) are provided. In one embodiment of the invention, the cells are melanoma cells, and the applied nsPEFs penetrate into the interior of tumor cells and cause tumor cell nuclei to rapidly shrink and tumor blood flow to stop. This new technique provides a highly localized targeting of tumor cells with only minor effects on overlying skin.