* Tariff and price floors target supply chains dominated by

China

* US solar manufacturers praise action as support for

domestic production and investment

* Implementation delayed until December 4

(Adds reactions from industries, quote from proclamation,

background)

By Nichola Groom and Alexandra Alper

WASHINGTON, Aug 6 (Reuters) - The White House on Thursday

imposed a series of price floors and a 15% tariff on products

made from polysilicon, the raw material used in semiconductors

and solar panels that is primarily produced by China.

U.S. President Donald Trump's proclamation under Section 232

of the Trade Expansion Act of 1962 is aimed at supporting

domestic chip and solar supply chains needed to compete with

Beijing on artificial intelligence and energy.

"The plan of action in this proclamation will, among other

things, help ensure the commercial viability of United States

production of polysilicon and its derivatives that is necessary

to meet United States economic and national security

requirements," the order said.

Polysilicon, an ultra-pure form of silicon, sits at the

start of the semiconductor and solar manufacturing supply

chains. Manufacturers turn silicon wafers into solar cells and

​then assemble those into panels used in solar projects.

American solar factories for the last decade have accused

their Chinese rivals of dumping solar panels in the market,

receiving unfair government subsidies and moving their

manufacturing to other countries to dodge U.S. tariffs.

The United States has two polysilicon factories. Hemlock

Semiconductor, which operates a plant in Michigan, is a joint

venture between Corning and Japan's Shin-Etsu Handotai

. Munich-based Wacker Chemie runs a factory in

Tennessee.

"Today's decision encourages continued investment in U.S.

capacity and supports long-term U.S. competitiveness," a Corning

spokesperson said.

Wacker said it was reviewing the actions to fully understand

their impact.

"We appreciate the Administration's continued engagement on

the issue given the ramifications for semiconductor supply chain

resilience, advanced computing infrastructure, and broader U.S.

defense and security interests," the company said in a

statement.

Domestic semiconductor manufacturing depends on solar

because the solar industry's larger demand for polysilicon helps

support production of the material required for chips. The chip

industry accounts for ​2.4% of global polysilicon demand,

according to the Semiconductor Industry Association.

U.S. solar ​manufacturing has expanded since Congress

created tax incentives ⁠in 2022. Much of that growth, however,

has been concentrated in panel assembly, leaving manufacturers

dependent on imported wafers and cells, which require longer

investment timelines.

Companies with U.S. solar factories, including T1 Energy ( TE )

, First Solar ( FSLR ) and Qcells, the U.S. solar arm of

South Korea's Hanwha, applauded Trump's move.

"This is a decisive win for advanced American manufacturing

and investment in domestic energy supply chains," Dan Barcelo,

CEO of T1 Energy ( TE ), said in a statement. In addition to its Texas

solar panel plant, T1 is investing $510 million in a cell

factory.

The trade protections will take effect on December 4, the

White House said.

Tim Brightbill, a trade attorney with Wiley Rein who has

brought several trade cases against Chinese solar companies,

warned that the delayed implementation could lead to a surge of

imports in the coming months.

Companies that buy solar panels have argued that the delay

is needed to adjust supply contracts to higher prices.

According to a White House document, the president set

minimum import prices of $21 per kilogram for polysilicon, $100

per kilogram for polysilicon ingots and wafers, $0.22 per watt

for solar cells and $0.38 per watt for solar modules, or panels.

The proclamation also authorizes the Commerce Department to

create an incentive program for companies that invest in

factories to produce polysilicon or derivative products.

The administration's plan to pursue a hybrid system

combining a minimum import price with tariffs was first reported

by Reuters.