Disclosed is a method for forming a low-k dielectric layer of a semiconductor device. The method includes a step providing a semiconductor substrate having a predetermined pattern, a step coating porous powders having a micro size on the semiconductor by spraying the porous powders, and a step performing a heat treatment process with respect to a resultant structure, thereby forming the low-k dielectric layer. After micro-sized porous powders are coated on a semiconductor substrate, a heat treatment process is performed, so that powders are bonded to each other, thereby forming a low-k dielectric layer even if the dielectric layer has a dielectric constant equal to or less than 2.8. A signal delay time is reduced by depositing the low-k dielectric layer on the semiconductor substrate.