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A VMOS (/ˈviːmɒs/) (vertical metal oxide semiconductor or V-groove MOS) transistor is a type of metal–oxide–semiconductor field-effect transistor (MOSFET). VMOS is also used to describe the V-groove shape vertically cut into the substrate material.^[1]

The "V" shape of the MOSFET's gate allows the device to deliver a higher amount of current from the source to the drain of the device. The shape of the depletion region creates a wider channel, allowing more current to flow through it.

During operation in blocking mode, the highest electric field occurs at the N⁺/p⁺ junction. The presence of a sharp corner at the bottom of the groove enhances the electric field at the edge of the channel in the depletion region, thus reducing the breakdown voltage of the device.^[2] This electric field launches electrons into the gate oxide and consequently, the trapped electrons shift the threshold voltage of the MOSFET. For this reason, the V-groove architecture is no longer used in commercial devices.

The device's use was a power device until more suitable geometries, like the UMOS (or Trench-Gate MOS) were introduced in order to lower the maximum electric field at the top of the V shape and thus leading to higher maximum voltages than in case of the VMOS.

The MOSFET was invented at Bell Labs between 1955 and 1960.^{[3][4][5][6][7][8]} The V-groove construction was pioneered by Jun-ichi Nishizawa in 1969,^[9] initially for the static induction transistor (SIT), a type of junction field-effect transistor (JFET).^[10]

The VMOS was invented by Hitachi in 1969,^[11] when they introduced the first vertical power MOSFET in Japan.^[12] T. J. Rodgers, while he was a student at Stanford University, filed a US patent for a VMOS in 1973.^[13] Siliconix commercially introduced a VMOS in 1975.^[11] The VMOS later developed into what became known as the vertical DMOS (VDMOS).^[14]

In 1978, American Microsystems (AMI) released the S2811.^[15][16] It was the first integrated circuit chip specifically designed as a digital signal processor (DSP), and was fabricated using VMOS, a technology that had previously not been mass-produced.^[16]