To be able to create small integrated wireless radio front ends, variablecapacitors that can be monolithically integrated on the same chip as theelectronic circuits are needed. Today’s radio front ends are based on solidstatediode varactors which suffer from poor tuning range and phase noiseand do not meet the requirements for a fully integrated wide band radiofront end. In this thesis we will look at possibilities for implementation ofa monolithic integrated MEMS varactor.A post-CMOS-MEMS process is used to manufacture the structures. Thepost-process is a combination of anisotropic RIE dry etch steps and anisotropic release step, which makes monlithic integration simple and lowcost. The actuation mechanism is based on an out of the plane curledcantilever beam. Initial curling of the structure as a result of residualstress in the CMOS layers of the chip is utilized to initially levitatethe actuator over the chip plane. To actuate the varactor combs, theactuator is heated with a joule-heating element placed under the structure.When the the actuator is heated to the in-plane alignment temperature,maximum capacitance is obtatined. Simulations and analytic models areused to predict the performance of the actuator and varactor. The analyticmodels presented and developed make development of out of plane curledvaractors more efficient and simpler than with FEM simulations only. Thecomplete varactor design was included in a test circuit sent to productionin November 2008.Simulations and models yield good results for tuning range and Qualityfactor.The tuning range is predicted to be between 240 % and 325 % andthe Q-factor is calculated to be firstname.lastname@example.orgGHz. The tuning voltage requiredfor operation of the varactor is within 8 V and the varactor does not sufferfrom pull-in, which is the case for electrostatic based varactors.