In spite of major progress in the science and technology of diamond growth, large-scale commercial production of gem-quality, large, single-crystal diamonds has not been feasible. Recently, we easily synthesized various types of gem-quality, large, single-crystal diamonds (Ib, IIa, and IIb) using a cubic high-pressure apparatus (performance enhanced by new design of double bevel hybrid anvil). Our solution saves the cost associated with the presses need, increases the region of synthesis of gem-quality, large, single-crystal diamonds, and decreases the effects of fluctuations of the pressure or temperature in the cubic sample cell. In addition, the quality and electrical properties of synthetic diamonds have been studied in detail. The synthetic diamonds have been successfully applied as diamond anvils or jewelry. This represents a relatively simple, inexpensive, and effective solution for commercial production and scientific research on gem-quality, large, single-crystal diamonds using a cubic high-pressure apparatus.