Based on my research, here are some of the major US microchip manufacturers:

Intel
Qualcomm
Texas Instruments
Micron Technology
Broadcom
NVIDIA Corporation
Advanced Micro Devices (AMD)
Applied Materials Inc.
Western Digital Corporation
Analog Devices
As for their nm scale, it varies from manufacturer to manufacturer and also depends on the specific products. However, some of the recent developments are:

Intel's 11th Gen processors are built on a 10nm process
Qualcomm's Snapdragon 888 uses a 5nm process
Micron's NAND flash technology goes down to 96-layer 3D NAND with a 0.11 um cell size
Regarding a comparison of US vs South Korean vs Japanese microchip industries, it's important to note that all three countries have a strong presence in the semiconductor market. However, here are some key differences:

The US is known for its expertise in the design and development of microchips, with many of the major manufacturers based there.
South Korea is home to Samsung and SK Hynix, two of the largest memory chip makers in the world. They have been focusing on developing advanced manufacturing processes for both memory and logic chips.
Japan is known for its innovations in materials science and has been a key player in the development of new types of semiconductors and memory technologies.
Overall, each country has its own strengths and areas of focus within the microchip industry.

According to the latest data available, the leading US microchip manufacturers are Intel, Qualcomm, and AMD. The current nm scale for these companies is as follows: Intel - 10nm, Qualcomm - 7nm, and AMD - 7nm.

In comparison, South Korea has major players such as Samsung Electronics and SK Hynix. 

The nm scale for Samsung Electronics is currently 5nm, whereas SK Hynix's nm scale is 10nm. 

Japan's microchip industry is dominated by companies such as Toshiba and Renesas Electronics. 

The nm scale for Toshiba is around 10nm, and Renesas Electronics has a range of nm scales between 250nm to 90nm based on the type of chip.

Overall, the US microchip industry is more advanced in terms of nm scale compared to that of South Korea and Japan.
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