Beyond the upper limit of the linear region of an ionization gauge, there is a falloff in the ion current with the increase of the measured pressure. This nonlinear behavior is to be expected by the theory of non-self-sutaining discharge, from which it follows that the pressure corresponding to the maxium of ion current may be expressed as p=E/C, where E is the field strength between the electrodes and C is a constant. Thus the upper limit, of the linear region will be extended as E increases.Four versions of gauge-electrodes configuration capable of giving higher field strength as well as maintaining lower sensitivity have been under test, leading to the result that the upper limit of linearity have extended from 10-1 Torr ab originc up to 1 Torr, 2 Torr, 6 Torr and 10 Torr, respeetively. There is satisfactory agreement between these experimental data and the calculated values based on the above theory.