Electric-field-directed growth and self-assembly of n-type, p-type, and p-n junction silicon nanowires by chemical-vapor deposition via the vapor-liquid-solid (VLS) growth mechanism in a low pressure chemical vapor deposition (LPCVD) system is demonstrated. The growth mechanism and electrical characteristics of p-n junction SiNWs are demonstrated. The technique of sample preparation to eliminate the noise for I-V measurement is discussed. Repeated and optical I-V measurement of p-n SiNWs is also demonstrated in this thesis. Electrostatic force microscopy (EFM) is used to spatially define the position of junction in the p-n junction SiNW.