An approach to optimize the electromechanical parameters of RF MEMS SPDT designed for operation at 10 GHz, using high dielectric constant material (HfO2) is presented and the results are compared to those for silicon dioxide - the conventional dielectric used for realizing capacitive shunt switches. The optimized length of CPW based transmission line (?/4), computed by considering the permittivity of gold at microwave frequencies is approximately 2700 ?m. The overall size of SPDT including the CPW ground area reduces from 12 mm2 for SiO2 dielectric layer based configuration to approximately 6 mm2 for HfO2 based capacitive SPDT. The reduction in dimensions ensures lower hysteresis in switch on-off characteristics and better stress related deformation control in electroplated metallic structures. The insertion loss, return loss and isolation are also better in the case of SPDT with HfO2 compared to SiO2 based devices. SPDT having SiO2 dielectric layer shows insertion loss of 0.35 dB, return loss of 26.4 dB and isolation of 45.1 dB at 10 GHz, whereas SPDT having HfO2 dielectric layer shows insertion loss of 0.08 dB, return loss of 35.7 dB and isolation of 48.8 dB at 10 GHz. Comparison of single switch response with different dielectrics is also presented.