Photodynamic therapy (PDT) is a very useful approach for cancer treatment, but it has a few short-term and long-term side effects arising from reactive oxygen species (ROS) generation. Recently a new photodynamic therapy (PDT) based not on the ROS generation capability of photosensitizers but on the heat generation capability of carbon nanotubes (CNT) combined with a near-infrared (NIR) light irradiation technique has received significant attention. Our experimental results show that PSi can also be utilized as a therapeutic agent that generates sufficient heat to kill cancer cells without toxicity. The surface temperature of PSi increases as high and as quickly as that of CNT, but PSi was found to produce a smaller amount of ROS than CNT during NIR light irradiation. In addition, we developed a new method to effectively measure the amount of the ROS produced by nanomaterial photosensitizers including porous silicon (PSi) and CNT. The analysis results show that this method is reliable and reproducible.