The Fujifilm X-T3 sensor is made by Sony not by Samsung. At Photokina 2018, in a recent interview with Managing Director of Fujifilm UK, the 26.1MP sensor inside the Fuji X-T3 is made by Sony and not by Samsung.
PGN interviewed Managing Director of Fujifilm UK – Theo Georgiades – about the Fujifilm GFX 50R and GFX 100S. And at the end of the interview, Theo Georgiades confirms that the 26MP sensor inside Fujifilm X-T3 is made by Sony, not by Samsung:
26MP Fujifilm X-T3 Sensor is Made by Sony
The 26.1-megapixel, X-Trans CMOS IV sensor on the Fuji X-T3 features a backside-illuminated design, a first for the X-mount lineup. The X-T3’s new sensor also comes with faster readout speeds, significantly reduces rolling shutter distortion.
From the interview:
Definitely not a Samsung sensor. It’s the same manufacturing process that we have gone through with all our other X-Trans sensors. Still designed and tested all by our R&D team.