Due to the trade-off relationship between breakdown voltage (BV) and specific on-resistance R_on,sp, to minimize the decrease in breakdown voltage while reducing on-resistance, an improved U-trench metal-oxide-semiconductor field-effect transistor (UMOSFET) structure with PN-Bottom is proposed. First, on the basis of traditional 100 V U-trench metal-oxide-semiconductor (UMOS) devices, deep trench etching technology is adopted to introduce a PN-Bottom wrapping region at the bottom of the trench, which wraps the P-type region inside the N-type region. Then, the new structural parameters and fabrication process of the device are introduced. Next, using the TCAD simulation tool, a detailed discussion was conducted on the doping concentration, width, and depth of the N-Bottom and P-Bottom encapsulation regions, and their effects on the breakdown voltage and specific on-resistance of the device were studied. Finally, the simulation results show that under the same conditions, an optimized design with BV of 110 V and R_on,sp of 1.15 mΩ·cm² was obtained.