The authors show that the incorporation of gain media in only a selected device area can annul the effect of material loss and enhance the performance of loss-limited plasmonic devices. In addition, they demonstrate that optical gain provides a mechanism for on/off switching in metal-dielectric-metal (MDM) plasmonic waveguides. The proposed gain-assisted plasmonic switch consists of a subwavelength MDM plasmonic waveguide side coupled to a cavity filled with semiconductor material. They show that the principle of operation of such gain-assisted plasmonic devices can be explained using a temporal coupled-mode theory.