In this paper, the necessity and theoretical analysis for Nanosecond-Scale Temperature Sensing Technology during Flat-Top Nanosecond Green Laser Annealing Process of Semiconductor Si-Wafer is overviewed. When a 532nm laser pulse with 10 ns or less pulse duration and several 100s mJ pulse energy is irradiated on the Si-wafer chip surface, the surface and internal temperature inside the chip is increased to several 100s or thousands quickly and cooled down during the next several 100s nanoseconds. The fastest commercial temperature sensor based on IR energy sensing has 40 us response time at which time the cooling process was already finished. So, the annealing process using 10 ns pulse laser annealing needs a proper method of ultrafast temperature measurement technology to understand the relationship between heated temperature and annealing quality which can make an impact on semiconductor chip performance. To resolve this issue, two-wavelength temperature measurement technology using fiber-guided sensing is selected among several technologies which is analyzed to know re-emission energy distribution from the Si-Chip and the captured energy into sensing fiber. Then, a proper focusing lens or lens set with optimum entrance pupil size to enhance the captured energy is determined. Then, a prototype setup for this two-tone temperature measurement is prepared and its performance is tried to compare with the results using a fast commercial temperature sensor.