A quantum information processor must perform accurate manipulations of many quantum degrees of freedom without introducing strong interactions with the environment that lead to the loss of quantum coherence. Spins in semiconductors have been shown to have long coherence times, so semiconducting quantum processors are feasible if the necessary manipulations can be performed without introducing excessive spin decoherence. To perform the necessary manipulations of single spins and to control the couplings between different spins, fine control of electronic energy levels and wave function overlaps is required. Electrically gated quantum dots have the promise of enabling such control, because the same gates that are used to define the quantum dot can be used to perform the necessary manipulations. This article describes recent progress toward the development of high-fidelity qubits using top-gate defined semiconductor quantum dots.