Heterojunction bipolar transistors (HBTs) feature high reverse current gains. The HBT are devices that have in their base region the semiconductor with a different bandgap than in the other regions. For example, Infineon's BFP840FESD (citing the product datasheet:
The BFP840FESD is a discrete RF heterojunction bipolar transistor
(HBT) with an integrated ESD protection suitable for 5 GHz band
), well, Infineon's BFP840FESD can have a
BF=946.1, as one can see in the BFP840FESD model:
GBJT 22 11 33 44 ID="Q1" TNOM=25 IS=2.009e-016 BF=946.1 &
NF=1 VAF=300 IKF=0.1993 ISE=6.26e-015 NE=2 BR=108 &
NR=1 VAR=1.288 IKR=0.0007328 ISC=8.126e-016 NC=2 &
RB=17 IRB=0 RBM=1 RE=0.05 RC=4.145 XTB=-2.276 &
EG=1.11 XTI=0 CJE=1.3e-013 VJE=0.6 MJE=0.5 TF=7.494e-013 &
XTF=17.49 VTF=0.5295 ITF=1.025 PTF=4.667 CJC=1.1e-014 &
VJC=0.67 MJC=0.88 XCJC=0.4894 TR=1.793e-009 CJS=3e-013 &
MJS=0.5 VJS=0.7 FC=0.352 KF=6.4e-012 AF=1.44
Of all the HBT flavors with this feature (abrupt junction, graded junction, graded base, double HBT), this feature is most pronounced in the double heterojunction bipolar transistor:
BF. The double HBT is a symmetrical device like unipolar transistors, although the HBT is definitely bipolar using both majority and minority carriers for the device operation. See the slides of the Purdue University course ECE606, Solid State Devices, Heterojunction Bipolar Transistor, pages 20 and 24.
Disclaimer: I have not found any evidence in the documentation indicating that the 2SC4713K is an HBT device.