  The single-shot readout data process is essential for the realization of
high-fidelity qubits and fault-tolerant quantum algorithms in semiconductor
quantum dots. However, the fidelity and visibility of the readout process is
sensitive to the choice of the thresholds and limited by the experimental
hardware. By demonstrating the linear dependence between the measured spin
state probabilities and readout visibilities along with dark counts, we
describe an alternative threshold-independent method for the single-shot
readout of spin qubits in semiconductor quantum dots. We can obtain the
extrapolated spin state probabilities of the prepared probabilities of the
excited spin state through the threshold-independent method. Then, we analyze
the corresponding errors of the method, finding that errors of the extrapolated
probabilities cannot be neglected with no constraints on the readout time and
threshold voltage. Therefore, by limiting the readout time and threshold
voltage we ensure the accuracy of the extrapolated probability. Then, we prove
that the efficiency and robustness of this method is 60 times larger than that
of the most commonly used method. Moreover, we discuss the influence of the
electron temperature on the effective area with a fixed external magnetic field
and provide a preliminary demonstration for a single-shot readout up to 0.7
K/1.5T in the future.
