This paper summarizes some of the main results obtained concerning aspects of anomalous single-dopant diffusion and the simultaneous diffusion of multi-diffusion species in semiconductors. Some important explanations of theoretical/practical aspects have been investigated, such as anomalous phenomena, general diffusivity expressions, general non-linear diffusion equations, modified Arrhenius equations and lowered activation energy have been offered in the case of the anomalous fast diffusion for single-dopant diffusion process. Indeed, a single diffusion process is always a complex system involving many interacting factors; conventional diffusion theory could not be applied to its investigation. The author has also investigated a system of multi-diffusion species with mutual interactions between them. More concretely, irreversible thermodynamics theory was used to investigate the simultaneous diffusion of dopants (As, B) and point defects (V, I) in Si semiconductors. Some attempts at theory development were made, such as setting up a system of general diffusion equations for the simultaneous diffusion of multi-diffusion species involving mutual interactions between them, such as the pair association and disassociation mechanisms which predominated during the simultaneous diffusion of dopants and point defects. The paper then gives some primary results of the numerical solution of distributions of dopants (B, As) and point defects (V, I) in Si semiconductor, using irreversible thermodynamics theory. Finally, several applications of simultaneous diffusion to semiconductor technology devices are also offered.