Because of moderate carrier concentrations (10@super 15@ - 10@super 20@ cm@super -3@), semiconductors and associated hetero- and nano-structures are suitable electronic systems to control both charges and spins by electromagnetic means. Particularly in magnetic semiconductors, manipulation of carrier spins can result in the cooperative and amplified effects through the spin exchange interaction between carrier spin s and local spin S. Those effects would open ways to develop multi-functional devices with low power consumption. One of such precursory demonstrations is the manipulation of magnetism with light in ferromagnetic III-V alloy semiconductors (In,Mn)As and (Ga,Mn)As. In this paper, we discuss the experimental results on (1) photo-generated carrier-induced ferromagnetism in p-(In,Mn)As/GaSb heterostructures, including ultrafast magnetic softening achieved in collaboration with Kono's group in Rice University, (2) collective rotation of ferromagnetically coupled Mn spins and its picosecond spin dynamics in ferromagnetic p-(Ga,Mn)As caused by the illumination with circularly polarized light without a magnetic field (optical spin injection), and (3) light-induced change in magnetic susceptibility at room temperature in GaAs-Fe composite structures, added with the demonstration of optically-controlled micro-cantilevers by Shinji's group of Tokyo Institute of Technology. Works towards room temperature ferromagnetism by other groups will also be reviewed. This work is supported in part by "Semiconductor Nanospintronics (02-)" of the Ministry of Education, Culture, Sports, Science and Technology, Japan.