A method of microwave assisted chemistry is disclosed in which power can be supplied more continuously at preferred power levels to more precisely control or moderate a chemical reaction. The method comprises measuring the duty cycle required to maintain a measured selected parameter of a sample at a predetermined set point while the sample is being exposed to microwave radiation at a first predetermined power level; and moderating the duty cycle and the applied microwave power to increase the on time of the duty cycle while applying power at a second predetermined power level that is sufficient to maintain the sample at the set point using the moderated duty cycle. A corresponding device for microwave assisted chemistry is also disclosed and comprises a cavity for receiving a sample, a waveguide connected to the cavity, a source of microwave radiation connected to the waveguide, and a switching power supply for driving the source of microwave radiation.