Microactuators are an integral part of some microelectromechanical systems where they perform different physical functions. Our research is dedicated to analysis and application of different actuation principles and to the design of custom structures for specific applications. Among principles of special interest for micromachined actuators are electrostatic, magnetic, piezoelectric and thermal actuation. Thermal actuation is the basis of actuators with bimetal effect, thermal pneumatic effects, shape memory alloys (SMA) and mechanical thermal expansion effect. Utilizing micromachining of silicon and glass we fabricated a MEMS actuator based on thermal expasion of paraffin as working fluid. The fabrication of this actuator comprised techniques of bulk micromachining of silicon and glass, annode bonding of silicon and glass, fabrication of thermal heater on metal film using vacuum sputtering and heater definition utilizing conventional photolithography, filling of chamber with paraffin and placement of an elastic PDMS membrane (polydimethylsiloxane). Single actuator elements are coupled into multielement batteries, thus enabling actuator function in steerable medical catheters.