We first report the formation and magnetic properties of MnAs and MnSb nanocrystals by "super Volmer-Weber epitaxy" utilizing very low surface energy substrates such as sulfur-passivated GaAs substrates. On the S-passivated GaAs surface MnAs dots with the size of about 16 nm and the density of 2x10(10) cm(-2) were successfully grown. SQUID analysis of these dots showed partly vertical easy magnetization axis. However, on the Se-GaAs surface, no MnAs dots were grown. SRPES revealed that Se atoms were segregated to the MnAs surface, probably playing a role of surfactant for the layer growth mode.