The traditional 6T SRAM (5T and a driving MOS transistor) OLED-on-silicon pixel circuit is taken as an example to analyze the influence of switch size on data writing. A novel digital OLED-on-silicon pixel circuit is proposed, which uses 5T (4T and a driving MOS transistor) to achieve the same function as 6T SRAM (5T and a driving MOS transistor). In addition, compared with the traditional SRAM structure, the data writing of the new pixel circuit is not affected by the switch size, and the smallest switch size can be used. Based on SMIC 0.18 μm 1.8 V/5 V mixed signal process design, the simulation results show that the minimum size of the switch in 6T SRAM pixel circuit is 540 nm/600 nm, and the pixel unit layout area is 4.3 μm × 4.3 μm. The switch in new 5T pixel circuit can be the minimum size of the process, that is, 300 nm / 600 nm, and the layout area is 3.91 μm × 3.91 μm. In contrast, the area of a single pixel unit layout is reduced by 17.3%.