A polarization-insensitive semiconductor optical amplifier (SOA) with a very thin active tensile-strained InGaAs bulk has been fabricated. The polarization sensitivity of the amplifier gain is less than 1 dB over both the entire range of driving current and the 3 dB optical bandwidth of more than 80 nm. For optical signals of 1550 nm wavelength, the SOA exhibits a high saturation output power +7.6 dBm together with a low noise figure of 7.5 dB, fibre-to-fibre gain of 11.5 dB, and low polarization sensitivity of 0.5 dB. Additionally, at the gain peak 1520 nm, the fibre-to-fibre gain is measured to be 14.1 dB.