Superjunction (SJ) structure is one of the most effective approaches to improving the performance limit between specific ON-resistance (

${R}_{\text {on,sp}}$

) and breakdown voltage (

$\textit {BV}$

) for the unipolar power device, particularly in high-voltage and high-current areas. In this letter,

${R}_{\text {on,sp}}-\textit {BV}$

performance limit of 4H-SiC SJ drift region is achieved featuring both the two-dimensional electric field and the anisotropy of impact ionization of 4H-SiC. The breakdown path is the curve from the bottom midpoint of N pillar to the top midpoint of P pillar via the midpoint of P-N pillar interface, instead of the midline of the pillar, due to that the impact ionization along [

$11~\overline {{2}}~0$

] is stronger than that along [0001]. Moreover, a design guideline is provided for optimized

${R}_{\text {on,sp}}$

(

${R}_{\text {on,opt}}$

) under a given

$\textit {BV}$

, including the width, depth, and concentration of SiC SJ drift region. SJ adoption enables SiC drift region to have a quasi-linear dependence of

${R}_{\text {on,sp}}$

$\textit {BV}$

, i.e.,

${R}_{\text {on,sp}}\propto \textit {BV}^{{1.007}}$

, which is well verified by TCAD simulation. With

$\textit {BV}$

larger than 2000V, the SJ utilization can significantly reduce

${R}_{\text {on,sp}}$

of SiC device. By determining the breakdown path, the theoretical performance limit shows huge potential of SJ approach for the high-voltage and high-current SiC device, and the practical design guideline can instruct to better design the SiC SJ device.

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