The changes of the electrical conductivity in chalcogenide amorphous semiconductors, $Ge_{1}Se_{1}Te_{2}$, have been studied. A phase change random access memory (PRAM) device without an access transistor is successfully fabricated with the $Ge_{1}Se_{1}Te_{2}$-phase-change resistor, which has much higher electrical resistivity than $Ge_{2}Sb_{2}Te_{5}$ and its electric resistivity can be varied by the factor of $10^5$ times, relating with the degree of crystallization. 100 nm thick $Ge_{1}Se_{1}Te_{2}$ thin film was formed by vacuum deposition at $1.5{ imes}10^{-5}$ Torr. The static mode switching (DC test) is tested for the $100;{mu}m-sized$ $Ge_{1}Se_{1}Te_{2}$ PRAM device. In the first sweep, the amorphous $Ge_{1}Se_{1}Te_{2}$ thin film showed a high resistance state at low voltage region. However, when it reached to the threshold voltage, $V_{th}$, the electrical resistance of device was drastically reduced through the formation of an electrically conducting path. The pulsed mode switching of the $20{mu}m-sized$ $Ge_{1}Se_{1}Te_{2}$ PRAM device showed that the reset of device was done with a 80 ns-8.6 V pulse and the set of device was done with a 200 ns-4.3 V pulse.