Remarkable variation of the sensitivity of a triode gauge with emission current and pressure was revealed to be due to the space charge effect of gas ions and electrons. An experimental attempt to reduce the space charge effect on the sensitivity was made. Triode gauges with a simple auxiliary electrode installed between the ion collector and the anode were fabricated and tested. The dependence of the sensitivity on emission current of the gauge was drastically reduced for most pressure ranges of high and medium vacuum. This result can be applied in the development of a new gauge with less dependence of the sensitivity on pressure.