Diamond is a widely-used industrial material that is attracting much attention due to its excellent physical properties such as high hardness, high Young’s modulus and high thermal conductivity. Among the various properties of diamond, negative electron affinity is what enables electrons to be emitted easily from diamond surface. Diamond is therefore highly expected to show good electron emitting characteristics during low-voltage, high-current operations. Sumitomo Electric Industries, Ltd. has been pursuing the development of diamond electron emitter that can be used as a new electron source for applications such as electron beam lithography, microwave tubes and integrated micro vacuum tubes. The authors had already developed a process for fabricating nano-size diamond tip emitters (1) which is a key technology for developing diamond electron emitter devices. A process for fabricating a 3-dimensional gate electrode for each emitter tip was also developed in order to control electron emission current at low voltages (2). Another key technology for providing high current electron source is the application of n-type diamond. For diamond to have electron conductivity, impurities must be doped into it. Compared to p-type diamond whose majority of carriers is holes, n-type diamond whose majority of carriers is electrons is more advantageous for emitting electrons at low voltages. P-type diamond exists naturally, and it can be easily grown artificially by the high pressure high temperature (HPHT) process or chemical vapor deposition (CVD) process. On the other hand, n-type diamond is difficult to be grown artificially. For example, when nitrogen is doped into diamond, a deep impurity level is exhibited and the doped diamond becomes almost an insulator. In recent years it was found that when phosphorus and sulfur are used as dopants, their doping efficiencies are very low and offer very high resistivity (3). It is reported, however, that n-type diamond synthesized in this manner has high electron emission properties (4). Sumitomo Electric had recently developed a technology for high density doping of phosphorus that allows n-type diamond to have low conductivity even at room temperature (5). Today, n-type diamond is being used as a material for low-voltage, high-current electron emitting sources. In this report, the authors show that n-type diamond has higher electron emission properties than ptype diamond under various surface conditions. The authors also report on the fabrication of high-current electron emitter device on n-type diamond using the uniform device fabrication technology reported previously.