\section{Method}

Single-crystalline $\beta $-EuP$_3$ was grown directly by reacting stoichiometric europium pieces and red phosphorus powder in a vacuumed fused silica ampoule.
The ampoule was slowly heated to 900 $^oC$ and after 24 hours it was cooled to 750  $^oC$ at a rate of  $3^oC/h$.
Then the furnace was switched off and cooled to room temperature.
The ampule was cracked open with caution in ethanol in order to avoid ignition of residual white phosphorus when exposed to air.
Powder X-ray diffraction measurement confirmed the $\beta $-phase of EuP$_3$ (See Fig. S1 in SI).
The obtained crystals have an easy cleaving plane along (001) direction, as evidenced by X-ray Laue back-scattering experiment.

In order to make an ohmic contact between the semi-conducting sample and leads, Ti/Au contacts were deposited with  $10~\mathrm{nm}$ Ti layer and  $80~\mathrm{nm}$ Au layer by electron-beam evaporator, and then the sample was annealed in rapid thermal processing system at 500 $^\circ C$ for 100~s.
Platinum wires were loaded on the contacts with silver paste in a four-terminal method ready for magneto-transport measurement.
The contact resistance was determined as tens of ohms leading to linear I-V curves at room temperature.
The electric transport measurements were performed in a PPMS-9 cryostat (Quantum Design, Inc) with a base temperature of 1.8~K and magnetic field up to 9~T.
Because the capacity of the PPMS for measuring resistance in a four-point fashion is limited to the order of $\mathrm{M}\Omega $ magnitude, we employed Keithley 6221 as a DC current source of $10~\mathrm{nA}$ and 6430 as a voltmeter for measuring the resistance of the low-temperature insulating state.
For instance, the temperature-dependent resistance in zero-field above 8~K was collected through PPMS, while the data acquisition at lower temperatures was switched to 6221 and 6430.
The magnetization measurements were preformed in an MPMS-3 SQUID VSM (Quantum Design, Inc) from 2 K to 300 K.

\section{Acknowledgment}
S. Jia thanks for helpful discussion with J. H. Chen, T. L. Xia and Y. G. Shi.
We notice the work on $\mathrm{EuAS_3}$ from Cheng \it et. al. \rm \cite{cheng2020magnetisminduced} during the preparation of this draft.
The work at Peking University was supported by the National Natural Science Foundation of China No.U1832214, No.11774007, the National Key R\&D Program of China (2018YFA0305601) and the Strategic Priority Research Program of the Chinese Academy of Science (Grant No. XDB28000000).
Experimental and theoretical work at Princeton University was supported by the Gordon and Betty Moore Foundation (Grant No. GBMF4547 and GBMF9461/Hasan)

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