The invention belongs to the semiconductor device field and discloses a junction field effect transistor. According to the junction field effect transistor, a back grid is formed between a trench and a P substrate of the JFET (junction type field effect transistor) and is corresponding to the position of a positive grid, and as a result, when negative voltage is applied to the grids, depletion regions of a positive grid PN junction and a negative grid PN junction do not horizontally extend, but vertically extend with the increase of the negative voltage, so that small pinch-off voltage can be obtained; drain-source voltage is mainly borne by horizontal extension of the depletion regions, and P type lightly-doped regions which are adjacent to a source are formed between the trench and the P substrate of the JFET, so that the distribution of an electric field in the trench of the JFET is more uniform, and N type lightly-doped regions which are located below a drain are formed between the trench and the P substrate of the JFET, and thus, breakdown of a PN junction formed by the trench and the P substrate of the JFET, which occurs at the bottom of a drain end, can be avoided, and as a result, high drain-source breakdown voltage can be obtained. With the junction field effect transistor adopted, contradictions among three parameters, namely, the pinch-off voltage, the drain-source breakdown voltage and current conduction capacity, can be alleviated.