A process for fabricating a heat sink with high-density parallel fins is provided. The process includes steps of providing a metal block including a first base and a second base, the first base being rectangular-solid shaped, the second base being rhombus-shaped and disposed over the first base wherein the second base includes a first edge surface and a second edge surface inclined at a specific angle, cutting the second base from a position on the top surface of the second base and parallel with the first edge surface until the first base is reached, thereby forming an inclined sheet, adjusting the inclined sheet to be normal to the top surface of the first base, thereby forming a fin, and repeating the cutting step and the adjusting step to produce the heat sink with high-density parallel fins.