Semiconductor thick film gas sensors based on tin oxide are fabricated and their gas response characteristics are examined for four simulant gases of chemical warfare agent (CWA)s. The sensing materials are prepared in three different sets. 1) The Pt or Pd $(1,;2,;3;wt.\%)$ as catalyst is impregnated in the base material of $SnO_2$ by impregnation method.2) $Al_2O_3;(0,;4,;12,;20;wt.\%),;In_2O_3;(1,;2,;3;wt.\%),;WO_3;(1,;2,;3;wt.\%),;TiO_2;(3,;5,;10;wt.\%)$ or $SiO_2;(3,;5,;10;wt.\%)$ is added to $SnO_2$ by physical ball milling process. 3) ZnO $(1,;2,;3,;4,;5;wt.\%)$ or $ZrO_2;(1,;3,;5;wt.\%)$ is added to $SnO_2$ by co-precipitation method. Surface morphology, particle size, and specific surface area of fabricated sensing films are performed by the SEM, XRD and BET respectively. Response characteristics are examined for simulant gases with temperature in the range 200 to $400^{circ}C$, with different gas concentrations. These sensors have high sensitivities more than $50\%$ at 500ppb concentration for test gases and also have shown good repetition tests. Four sensing materials are selected with good sensitivity and stability and are fabricated as a sensor array A sensor array Identities among the four simulant gases through the principal component analysis (PCA). High sensitivity is acquired by using the semiconductor thick film gas sensors and four CWA gases are classified by using a sensor array through PCA.