High purity silicon used for photovoltaic application, namely solar grade silicon (SOG-Si) , has been commercially supplied mainly from the off-grade high purity silicon manufactured by the Siemens process. However, recent and rapid growth in solar cell production has induced a serious shortage of SOG-Si. With an aim of resolving low productivity of the Siemens process, various types of SOG-Si production/purification processes have been invented as a post-Siemens process. Some processes are coming under development aiming at establishment of new commercial process. These processes can be classified into the following three technologies: (1) decomposition and/or hydrogen reduction of silane gases by improving the current commercial Siemens-based processes, (2) metallothermic reduction of silicon halide compounds by zinc or aluminum, and (3) upgrading metallurgical-grade silicon by employing metallurgical purification methods.<BR>This paper reviews various types of SOG-Si production processes, particularly the processes based on the hydrogen reduction and/or thermal decomposition of silicon halides and silane gases. These reduction processes are classified from the viewpoint of the silicon compounds and reaction types, and the features of the processes are analyzed. The future prospect for the development of new high purity silicon production process is presented.