Commercial Light-Emitting Diodes (LEDs) exhibit a -3 dB modulation bandwidth of only several MHz, which severely affects the information capacity and transmission in visible light communication. In this study, to fabricate an LED with high bandwidth, the influencing factors and mechanism of the modulation bandwidth of an LED device were investigated. Three LED chips with PN junction areas of 200 μm×800 μm, 300 μm×900 μm, and 300 μm×1 200 μm were designed and fabricated. By analyzing the photoelectric and modulation characteristics of the three LEDs, the relationship between the PN junction area and the modulation bandwidth was determined. Then, the capacitance-voltage curves of the three samples were compared, and the influence of the capacitance on the modulation bandwidth was analyzed. The results indicate that the LED with a PN junction area of 200 μm×800 μm exhibits the minimum capacitance, resulting in the maximum -3 dB bandwidth of 49.9 MHz among the three LEDs. This demonstrates that the parasitic capacitance caused by package, LED drive circuits, etc., has a significant effect on the modulation bandwidth of LEDs. Thus, LED devices with high bandwidth can be fabricated by decreasing the parasitic capacitance of the LED.