A capacitor having a suitably large value for decoupling applications is formed in a trench defined by isolation structures such as recessed isolation or shallow trench isolation. The capacitor provides a contact area coextensive with an active area and can be reliably formed individually or in small numbers. Plate contacts are preferably made through implanted regions extending to or between dopant diffused regions forming a capacitor plate. The capacitor can be formed by a process subsequent to formation of isolation structures such that preferred soft mask processes can be used to form the isolation structures and process commonality and compatibility constraint are avoided while the capacitor forming processes can be performed in common with processing for other structures.