Interdigital electrodes/contacts (IDCs) based sensors are widely used in a variety of chemical and biological sensors, which presents promising advantages such as high sensitivity, low electron mobility, enhanced gate conductivity and increased signal to noise ratio. In particular, interdigitating (or interlocking) the electrodes can be valuable for organic field-effect transistors (OFET) designed using conducting polymers and peptides as semiconducting material. The current chapter discusses the finite-element numerical modelling along with the design and fabrication of IDC-based OFETs.