A method for manufacturing a transistor is provided to prevent residual of a gate conductive layer by forming a spacer on a part where bowing phenomenon is generated. A semiconductor substrate(41) having an active region and an isolation region is provided. The substrate of the isolation region is etched to form a trench(T'). A floating dielectric is formed on a lower portion of the isolation region. A dielectric is formed on the floating dielectric so that the trench is gap-filled to form an isolation layer(47). Partial regions of the dielectric and the floating dielectric are etched to partially expose a side of the active region. A spacer later(48) is formed on a side of the floating dielectric that is not etched. A gate(52) is formed on the resultant substrate structure including the spacer layer formed at the side of the floating dielectric.
