Silicon epitaxial diode rectifier chips are semiconductor devices that are used to rectify AC voltage to DC voltage in electronic circuits. They are made from a silicon substrate with an epitaxial layer that is doped to form a p-n junction. The rectifier chip has a specific voltage rating and can handle a certain amount of current. The diode rectifier chips are used in a wide range of applications, including power supplies, voltage regulators, and inverters. They are popular due to their high efficiency and low cost.