The yield response factor of semi-dwarf winter wheat was determined from field experimental data conducted during three consecutive years (2002-03 to 2004-05). The yield response factor (ky) varies depending on growth phases and also among seasons. On an average, the ky for early, vegetative, booting-heading, and flowering-soft dough stages were 0.27, 0.21, 0.25, and 0.17, respectively. According to the value of yield response factor, the most sensitive growth stages were in the order: CRI> booting-heading>maximum tillering> flowering-soft dough. For the alternate deficit strategies (deficit at tillering + flowering –soft dough; deficit at CRI + booting-heading stages), the ky values were 0.77 and 0.61, respectively. For the whole growing period, the ky values were 1.58, 0.43, 2.29, and 0.61 for deficit at early, vegetative, booting-heading, and flowering-soft dough stages, respectively. The sensitivity index (lembda i, of Jensen model) for early, vegetative, booting-heading, and flowering-soft dough phases were 0.35, 0.22, 0.31, and 0.14, respectively. A more sensitive growth stage has a higher value of lambda i, and therefore water supply is more important at early and booting-heading phases.