To realize p-bits that fluctuate between 0 and 1 with precisely controlled probabilities, stochastic oscillation behavior of threshold switch (TS) device was induced by applying supply voltage ($\mathrm{V}_{\mathrm{D}\mathrm{D}}$) near-threshold voltage ($\mathrm{V}_{\mathrm{T}\mathrm{H}}$). Insulator-metal transition (IMT) device and ovonic threshold switch (OTS) device were investigated as a source of p-bit generation. It was confirmed that a small voltage change of mV-scale in the near-threshold region can give a high degree of stochasticity to the oscillation frequency. Also, the probability was controlled by a comparator and shift of a compare-voltage ($\mathrm{V}_{\mathrm{comp}}$) with excellent controllability. Finally, a simple probabilistic Boolean logic operation was tested by 100 p-bits generated from IMT devices.